This US-Thai collaborative program is designed to provide epidemilogic and immunologic information required for improved prevention or treatment of leprosy, and to provide better pharmacologic data for the use of common drugs in tropical areas of the world. The program is built upon the long-standing collaboration between the faculties of The University of Illinois College of Medicine and Chiang Mai University in northern Thailand. The Illinois core facility is the US center and includes laboratories for training Thai workers for work to be done in Thailand. The Chiang Mai core is the Thai laboratory and clinical facility. McKean Rehabilitation Institute, Chiang Mai, will provide access to 300 leprosy inpatients and 2000 outpatients through its associated villages and clinics. The component projects will investigate leprosy from epidemilogic, genetic, and immunologic viewpoints. M. leprae specific and nonspecific antibody, lymphocyte, and phagocytic cell responses will be characterized using techniques from the Universtity of Kentucky, and the University of Illinois. Studies of the role of immune complexes in leprosy and its complications including glomerulonephritis and erythema nodosum leprosum will be based at the University of New Mexico. All component projects involve Thai co-investigators who, after training in the US, will implement the research in Thailand.